Active display system and method with optical addressing

ABSTRACT

A display system, including an optical transmitter configured to optically transmit digital image information associated with an image to be displayed. The system also includes an active display including a decoder electrically coupled with a plurality of display elements that are configured to produce visible light in response to electrical stimulation. The decoder is configured to receive the digital image information and in response produce a control signal for each of the display elements, the control signals being usable to individually control visible light produced by the display elements so as to cause display of the image.

BACKGROUND OF THE INVENTION

Various techniques exist for displaying still and moving images. Onesuch technique involves the use of passive optical projection systems,which commonly employ a projector in connection with a passive displayscreen. In passive systems, all of the optical energy to display animage is typically generated by the projector. This often requires useof expensive bulbs or lamps that can consume a significant amount ofpower and generate excessive heat. Many systems employ cooling fans todissipate the excess heat. The cooling fans often produce undesirablenoise, in addition to adding to the manufacturing expense and complexityof the projection system. In addition, passive systems commonly employmirrors, color wheels, polarizers and other optical components betweenthe light source and the display screen. These components can increasethe expense of the system, degrade image quality, and make it difficultto maintain image quality when producing images of varying size and/orbrightness.

SUMMARY OF THE INVENTION

A display system is provided, including an optical transmitterconfigured to optically transmit digital image information associatedwith an image to be displayed. The system also includes an activedisplay including a decoder electrically coupled with a plurality ofdisplay elements that are configured to produce visible light inresponse to electrical stimulation. The decoder is configured to receivethe digital image information and in response produce a control signalfor each of the display elements, the control signals being usable toindividually control visible light produced by the display elements soas to cause display of the image.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic depiction of an active display system according toan embodiment of the invention.

FIG. 2 is a schematic depiction of an exemplary sub-array that may beimplemented in connection with the system of FIG. 1, together with imageinformation used to control operation of the sub-array.

FIG. 3 schematically depicts a structure and methodology that may beused with the sub-array of FIG. 2 to process an incoming serialbitstream of image information.

FIG. 4 is a schematic depiction of an exemplary group of emissiveelements that may be implemented in connection with the embodiments ofFIGS. 1 and 2.

DETAILED DESCRIPTION

The invention is directed to a method and apparatus for displayingimages. In this context, images may include still images or video imagesand, for consistency, will be referred to herein as images.

FIG. 1 depicts a display system 10 for displaying images. System 10includes an optical transmitter 12 and an active display 14. Opticaltransmitter 12 optically transmits image information 16 for receipt atactive display 14. Active display 14 responds to the image informationin order to actively display an image based on image information 16.

Active display 14 typically includes a plurality of display elementsthat are controlled based on image information 16 to produce an image.For example, in the depicted exemplary embodiment, active display 14includes a plurality of emissive components configured to emit visiblelight. The quality of the light produced by each of the individualemissive components determines how the overall image will appear to theviewer. As explained in more detail below, the state of each emissivecomponent may be individually varied to control the color, brightnessand other characteristics of the light produced by the emissivecomponent.

For moving images, the states of the individual emissive components arechanged periodically to create the moving image. For example, theintensity of a particular emissive component may be varied at regularintervals known as frames. A typical frame rate in video applications is60 frames per second. In such an application, controlling the state ofeach individual emissive component over a number of successive framesproduces, from the viewer's perspective, a moving image.

As indicated above, optical transmitter 12 provides the information thatis used to control the states of the individual emissive components inactive display 14. In contrast to the projectors that are often used inpassive systems, optical transmitter 12 normally is not configured toproject light of sufficient intensity to produce a viewable image on apassive screen or other passive display device. As such, opticaltransmitter 12 may not need to employ expensive, high-intensity bulbs,such as those commonly used in passive systems to produce the light thatforms the displayed image. Nor does optical transmitter 12 necessarilyneed to employ the cooling fans associated with such systems, or themirrors, lenses and other optical devices often used in passive systems.Instead of using high-intensity light, optical transmitter 12 typicallyconveys image information 16 to active display 14 via low intensitylight, as explained in more detail below.

Optical transmitter typically includes one or more emitters 18, or likeoptical transmission devices configured to transmit image information 16via low intensity light. The image information typically is transmittedas a number of spatially separated beams 20 of low-intensity infraredlight, with each beam corresponding to a portion 22 of active display14. Particular beams 20 and corresponding display portions 22 areindividually designated with letters (a, b, etc.) following thereference number. As explained in more detail below, each beam typicallyincludes a serial bitstream of digitally encoded information, which maybe used to control behavior of the emissive components in a givenportion of active display 14.

Portions 22 may also be referred to as sub-arrays of active display 14.In the depicted example, each beam 20 carries image informationcorresponding to a portion of the overall image to be presented on thecorresponding sub-array 22. For example, beam 20 a corresponds tosub-array 22 a and carries information used to produce images on thatsub-array. Each sub-array includes a decoder or like processingsubsystem that is configured to receive the image information encodedwithin the low intensity light beam. Upon receiving the beam, thedecoder processes the encoded image information to produce individualcontrol signals for the various emissive components contained within thesub-array. Based on the control signals produced within each sub-array,the sub-arrays collectively produce the overall image presented to aviewer by active display 14.

As seen in FIG. 1, display system 10 may be implemented as a frontprojection system, in which the viewer is on the same side of activedisplay 14 as optical transmitter 12. Display system 10 may also beimplemented in a rear projection configuration, in which the opticaltransmitter and viewer are on opposite sides of the active display.Generally, the viewer, optical transmitter and active display may be ina desired relative orientation that allows the transmitter to opticallytransmit image information to the active display.

It should be appreciated that the individual sub-arrays are opticallyaddressed, instead of electrically addressed. In this context,“addressing” refers to the manner in which image information isdelivered to a particular component of display system 10. In thedepicted embodiment, optical transmitter 12 optically addressessub-arrays because it delivers image information 16 via opticaltransmission, instead of with a wired electrical coupling. Though thesub-arrays are normally optically addressed, the individual emissivecomponents within a sub-array often are electrically addressed, as willbe explained below.

Active display 14 may include a single sub-array 22, or any other numberof sub-arrays, as desired. Display system 10 is extremely flexible, inthat it is relatively simple to change the size of the display by simplyadding sub-arrays 22. To accommodate the added sub-arrays, transmitter12 may be easily reconfigured to provide image information to the newsub-arrays. The optical addressing methods described above greatlysimplify varying the display size, because no physical reconfigurationof the addressing connections is necessary. In addition, the opticaladdressing allows the density of emissive components in the sub-arraysto be increased without significantly increasing the overall complexityof the system. By contrast, in electrically addressed systems, addingemissive components (e.g., to increase display size or brightness)requires physical reconfiguration of the addressing circuitry, andusually involves a significant increase in the overall complexity andmanufacturing expense of the display system.

It should be understood that one or more beams 20 of image informationmay be used. Often it will be desirable to have the beams and sub-arraysin a one-to-one relationship, such that each beam carries imageinformation for a single designated one of the sub-arrays.Alternatively, image information for a particular sub-array may becontained in multiple beams 20. Yet another alternative is to have anindividual beam carry image information for multiple sub-arrays. In sucha case, the beam is aimed at the multiple sub-arrays so that each of thecorresponding sub-arrays can receive the information. The digitalinformation encoded in the beam includes addressing/header informationwhich enables each of the receiving sub-arrays to identify and processthe respective portions of the image information in the beam.

FIG. 2 schematically depicts an individual sub-array 22, along withimage information 28 used to control operation of the sub-array. Asindicated, sub-array 22 typically includes a decoder 30 electricallycoupled with a number of display elements such as emissive components32. Decoder 30 receives and processes image information 28, so as toproduce control signals corresponding to the emissive components coupledwith the decoder. These control signals control visible-spectrum lightproduced by the emissive components, and thus control the image producedby sub-array 22.

Emissive components 32 may be of any suitable construction or type,provided they are capable of producing visible-spectrum light to form animage. The depicted embodiment includes red (R), green (G) and blue (B)emissive components organized into pixels, with each pixel containingone of each color component. For example, components R1, G1 and B1collectively form a pixel; R2, G2 and B2 form another pixel.Alternatively, in other embodiments, a pixel may consist of only asingle display element (e.g. an individual emissive component). Theindividual components in each pixel may be referred to as sub-pixels,and typically are independently controlled as explained below in orderto vary the color and intensity of the light produced by the pixel. Asindicated, any number of emissive components and pixels may be providedin a sub-array. Also, colors other than red, green and blue may be used,such as white, cyan, magenta, yellow, etc. Furthermore, althoughemissive components are described herein, transmissive components (suchas in an LCD), reflective components (such as in e-paper) or any numberof other components capable of controlling light may be used.

As indicated, decoder 30 typically is coupled with the emissivecomponents of sub-array 22 via an electrical connection such as coupling34. A wide variety of coupling methods and topologies may be used. Asseen in the depicted embodiment, it will often be appropriate to useparallel address lines 36 running between decoder 30 and each of theemissive components, with an individual address line being provided foreach emissive component. Alternatively, a bus arrangement or other typeof topology may be employed to electrically connect the decoder andemissive components.

As indicated above, decoder 30 receives digital image information inoptic form and converts that information into control signalscorresponding to emissive components 32 of sub-array 22. Typically, thisconversion is implemented as a serial-to-parallel conversion, asschematically illustrated in FIG. 3. Specifically, decoder 30 receivesimage information in the form of a serial bitstream of digitally encodedinformation. This bitstream may include various types of informationrelating to the image to be displayed. For example, the bitstream mightspecify that a particular emissive component is to be activated at aparticular intensity during an upcoming video frame. In any event, asindicated, the serial bitstream is decoded and separated into multiplecontrol signals that are delivered in parallel to a plurality ofemissive components.

Referring again to FIG. 2, the figure also shows image information 28being provided to sub-array in the form of a serial bitstream 40. Asshown, it will often be desirable to organize the image information inbitstream 40 into sequential frame segments F1, F2, F3, etc. Each framesegment includes image information corresponding to the image to bedisplayed by sub-array 22 during a given video frame. For example, F1contains information for a first frame, F2 for a second successiveframe, F3 for the next frame, and so on. As this information is receivedby decoder 30, it is successively processed and employed to control theimages produced on sub-array 22 during a series of sequential videoframes.

The frame segments typically include information corresponding to eachof the individual emissive components within the sub-array. For example,as indicated, segment F1 contains information corresponding to emissivecomponents R1, G1, B1, R2, G2, B2, etc. Such information may, forexample, specify the intensity for the corresponding emissive componentsduring the F1 frame. Alternatively, the bitstream may be organized bypixel, sub-pixel or according to other data structures or schemes.

Referring specifically to decoder 30, the decoder typically includessome form of optical receiver 42 to receive the incoming optical imageinformation 28. This may be implemented with a phototransistor,photodiode or like device. Receiver 42 is configured to receive theincoming digital bitstream and convert the digital pulses intoelectrical signals used to control the emissive components of thesub-array 22. The conversion may be effected by the receiver alone, orin combination with other components.

Decoder 30 also performs an address decoding function, to ensure thatcontrol signals are supplied to appropriate emissive components 32 insub-array 22. Various decoding/addressing schemes may be used. Forexample, a relatively simple scheme would be to assign the first N bitsin a frame to the first pixel (R1, G1, and B1), the second N bits to thenext pixel (R2, G2, and B2), and so on. Alternatively, the imageinformation for a given emissive component may include not onlybrightness/color information, but also address information thatspecifies the particular address lines 36 that are to be used to controlthat emissive component.

Decoder may also include a controller 44, storage 46, and/or variousother components to aid in the receiving, decoding, addressing and otherfunctions described above. Storage 46, for example, may be used toprovide a temporary buffer to hold control signals until all of thecontrol signals are ready for simultaneous parallel delivery to emissivecomponents 32. Controller 44 may assist in synchronized delivery of thecontrol signals through issuance of synchronization signals. The decoderthus may be responsive to synchronization signals to synchronizeapplication of the control signals to the emissive components.

Referring now to FIG. 4, exemplary red, green and blue emissivecomponents of a representative pixel 48 are depicted. As indicated, eachincludes a light-emitting device that is controlled via application of acontrol signal. Referring specifically to the red portion of the pixel,a red light-emitting diode (LED) 50 is coupled between positive supply52 and ground 54. LED 50 is in series with a switch, such as transistor56, which is responsive to control signal 58 in order to control thecurrent flowing through the LED.

Typically, control signal 58 is provided during a given video frame asone or more fixed amplitude voltage pulses having a fixed time duration.The voltage pulses are provided to the emissive components via theelectrical connections between decoder 30 and emissive components 32(FIG. 2). The number of pulses occurring within a frame then determinesa characteristic of light produced by the LED for that frame, forexample, light intensity.

The relationship between the control signal and the light produced by agiven pixel within a video frame may be more clearly understood in thecontext of a 24-bit RGB color system. In such a system, 8 bits areprovided for each of the red, green and blue emissive components of agiven pixel. Thus, 256 intensities of red are available, as are 256intensities of green and blue. This yields 256×256×256, or roughly 16.8million combinations of intensities for the three components. Suchsystems are often referred to as providing 16.8 million colors.

To accomplish 256 gradations for each of the colors, the video frame isdivided into 255 intervals. During each such interval, a fixed amplitudevoltage pulse may be applied to the switch that controls the currentthrough the respective LED (e.g., transistor 56). To provide varyingintensities of red light during a frame, the switch would be pulsed fromanywhere between 0 and 255 of the available time intervals. No pulsewould mean no red contribution to the pixel during that frame. 255pulses would be the maximum contribution of red to the pixel.

Control signal 58 may be considered a duty-cycle modulated pulse train.As explained above, the digital image information for the depictedsub-array includes intensity information for each of the emissivecomponents in the sub-array. This intensity information is used tomodulate the duty time of the control signal for the frame. In otherwords, as the intensity specified by the image information for a givenemissive element increases, such as with pulse width modulation, theamount of time that control signal 58 is pulsed high during the givenframe increases. In the depicted example, the individual pulses are offixed duration (width), so increasing the duty time for a given frameinvolves increasing the number of pulses that are applied to transistor56 during that frame. Various such methods may be employed, includingpulse width modulation, pulse position modulation, etc.

For typical frame rates, such as 60 frames per second, the pulsesnormally can occur at any time during the frame, and multiple pulsesneed not be symmetrically spaced in time. For example, at 60 frames persecond in a 24-bit system as described above, assume that the imageinformation specifies a red intensity value of 4, on a scale from 0 to255. This equates to a control signal 58 that is pulsed 4 times duringthe frame. These 4 pulses can occur clumped together in adjacent timeintervals, evenly distributed through the frame, or at any otherrelative time, because the human eye typically will not perceive thedifference at a frame rate of 60 frames per second.

It should be appreciated that the above system provides for control overboth the color and brightness of a given pixel. For example, in the24-bit example given above, a pixel with an RGB value of 128-128-128typically would be the same hue as a pixel with an RGB value of 4-4-4,because the relative contributions of the three emissive components areequal. However, the 128-128-128 pixel would be much brighter.

It should be further understood that any desired color depth may beused, and the above 24-bit system is provided merely as an example. Moreor less than 8 bits may be used to specify the number of intensitygradations for a given emissive component.

Additionally, or alternatively, analog methods may be used to controlthe intensity of the light produced by the LEDs. For example, instead ofusing fixed amplitude voltage pulses to intermittently activate the LEDswitches, decoder 30 may be configured to provide variable amplitudecontrol signals to the LED switches. Referring specifically to red LED50, the intensity during a given interval would be controlled byapplying a voltage during the entire duration of the video frame. Thelevel (amplitude) of this voltage would be increased or decreased tovary the intensity to a desired level.

While the present invention has been particularly shown and describedwith reference to the foregoing preferred embodiments, those skilled inthe art will understand that many variations may be made therein withoutdeparting from the spirit and scope of the invention as defined in thefollowing claims. The description of the invention should be understoodto include all novel and non-obvious combinations of elements describedherein, and claims may be presented in this or a later application toany novel and non-obvious combination of these elements. Where theclaims recite “a” or “a first” element or the equivalent thereof, suchclaims should be understood to include incorporation of one or more suchelements, neither requiring nor excluding two or more such elements.

1. A display system, comprising: an optical transmitter configured tooptically project digital image information associated with an image tobe displayed; and an active display including a decoder coupled with aplurality of display elements that are configured to produce visiblelight, where the decoder is configured to receive the projected digitalimage information and in response produce a control signal for each ofthe display elements, the control signals being usable to individuallycontrol visible light produced by the elements so as to cause display ofthe image.
 2. The display system of claim 1, where the opticaltransmitter is configured to transmit the digital image information viainfrared light as a serial bitstream.
 3. The display system of claim 2,where the decoder is configured to generate the control signals based onthe serial bitstream and apply such control signals in parallel to theplurality of display elements.
 4. The display system of claim 1, wherethe decoder includes a storage configured to store the digital imageinformation or control signals prior to application of the controlsignals to the display elements.
 5. The display system of claim 1, wherethe decoder is configured to be responsive to a synchronization signalto synchronize application of the control signals to the displayelements.
 6. The display system of claim 1, where the image informationincludes intensity information for each of the display elements, andwhere the decoder is configured to use such intensity information toduty-cycle modulate a pulse train for each display element, the pulsetrain being operable to intermittently activate the respective displayelement.
 7. The display system of claim 1, where some of the displayelements are configured to produce red light, some of the displayelements are configured to produce green light, and some of the displayelements are configured to produce blue light.
 8. The display system ofclaim 7, where groupings of the display elements define pixels, witheach pixel containing red, green and blue sub-pixels.
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 19. Adisplay system, including: transmission means for optically projectingimage information associated with an image to be displayed; and anactive display including a plurality of sub-arrays, each having: visiblelight-producing means for producing visible light in response toelectrical stimulation; and decoder means for optically receiving aportion of the projected image information and generating a plurality ofcontrol signals based on such portion of the image information, thedecoder means being coupled with the visible light-producing means andconfigured to apply the control signals to the visible-light producingmeans so as to cause display of a portion of the image.
 20. The displaysystem of claim 19, where the transmission means includes an opticalprojector configured to project the image information with infraredlight via one or more serial bitstreams.
 21. A method of activelydisplaying an image, comprising: optically projecting digital imageinformation associated with an image to be displayed; opticallyreceiving the projected digital image information at an active displaydevice; processing the digital image information to generate a pluralityof electrical control signals that each correspond to one of a pluralityof individual emissive display elements provided on the active displaydevice; and applying the electrical control signals to the emissivedisplay elements to control visible light produced by the emissivedisplay elements and thereby display the image.
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